TTL to Line out / Line out to TTL schematic

All you need to do for the conversion of TTL to line level signal is to drop the signal level somewhat and put a suitable capacitor in series.

For example youi can try 4.7 kohm resistor from TTL output to a common point. Then 1 kohm from this common point circuit ground. Then a suitable capacitor, for example 10 uF or larger from the common point to line output (if you use electrolytic capacitor put it such way that + points to that common point).

This converts the TTL output signal to the signal quite comparable to level typical to audio signal.

Rwemeber that this method does not pass the static logic state information, juts the signal state changes information.

Other idea if the logic state is necessary is to use the TTL outptu control to turn some auitable audio frequency oscillator on/off (for example logic 1 = audio output on).

Here are fre idea.

If you want a more or less reliable way to retreive digital data from an audio device you will need to convert the digital data into some form of sound and back.

Take a look at Kansas City tapes on

like to

computer.

That won't work unless the TTL Signal is encoded correctly.

You need to tell us more about the frequency of the data and how it's encoded. If you have a low enough bit rate you might get away with a simple Voltage Controlled Oscillator (VCO) and a Frequency to Voltage Converter.